Effect of a dielectric substrate with a subwavelength thickness on light diffraction by rectangular hole arrays on metallic film

Abstract

A theoretical study of the effect of ultrathin dielectric substrate in THz wave diffraction phenomena on a subwavelength nanostructured system is conducted. The proposed system is composed of a dielectric substrate with a thickness of ∼ λ/1000 and a subwavelength-scaled rectangular hole array on a metal thin film in THz wavelength region. A modified Rayleigh diffraction theory has been developed to take into account the contribution of reflection at the air-substrate interface. A calculation of the terahertz transmission while varying the thickness shows that the effect of a thin dielectric substrate starts to vanish when the thickness becomes ∼1/100 of the incident light’s wavelength. Theoretically, the results are well explained because most electric fields are confined near the rectangular aperture, which results in the dominant existence of the field inside the thin substrate. Additionally, the effect of a thin dispersive substrate is discussed.